Using isolated epitaxial structures in glue bonding for multiple group-iii nitride leds on a single substrate

ABSTRACT

A method for forming a plurality of semiconductor light emitting devices includes forming an epitaxial layer having a first type doped layer, a light emitting layer, and a second type doped layer on a first temporary substrate. The epitaxial layer is separated into a plurality of epitaxial structures on the first temporary substrate. A second temporary substrate is coupled to the epitaxial layer with a first adhesive layer and the first temporary substrate is removed from the epitaxial layer. A permanent semiconductor substrate is coupled to the epitaxial layer with a second adhesive layer. The second temporary substrate and the first adhesive layer are removed from the epitaxial layer. The permanent semiconductor substrate is separated into a plurality of portions with each portion corresponding to at least one of the plurality of epitaxial structures to form a plurality of semiconductor light emitting devices.

BACKGROUND

1. Field of the Invention

The present invention relates to a semiconductor light emittingcomponent, and more particularly to a light emitting diode (LED) arrayand a method for manufacturing the LED array.

2. Description of Related Art

FIG. 1 illustrates a schematic view of a conventional horizontal lightemitting diode. Referring to FIG. 1, horizontal light emitting diode 100includes epitaxial substrate 102. Epitaxial structure 104 is grown fromthe epitaxial substrate by an epitaxial growth process. Electrode unit106 is formed on the epitaxial structure for providing electricalenergy. Epitaxial substrate 102 is made of a material such as sapphireor SiC so that epitaxial growth of group-III nitride (e.g.,gallium-nitride-based (GaN-based) or indium-gallium-nitride-based(InGaN-based) semiconductor material) can be achieved on epitaxialsubstrate 102.

Epitaxial structure 104 is usually made of GaN-based semiconductormaterial or InGaN-based semiconductor material. During the epitaxygrowth process, GaN-based semiconductor material or InGaN-basedsemiconductor material epitaxially grows up from epitaxial substrate 102to form n-type doped layer 108 and p-type doped layer 110. When theelectrical energy is applied to epitaxial structure 108, light emittingportion 112 at junction of n-type doped layer 108 and p-type doped layer110 generates an electron-hole capture phenomenon. As a result, theelectrons of light emitting portion 112 will fall to a lower energylevel and release energy with a photon mode. For example, light emittingportion 112 is a multiple quantum well (MQW) structure capable ofrestricting a spatial movement of the electrons and the holes. Thus, acollision probability of the electrons and the holes is increased sothat the electron-hole capture phenomenon occurs easily, therebyenhancing light emitting efficiency.

Electrode unit 106 includes first electrode 114 and second electrode116. First electrode 114 and second electrode 116 are in ohmic contactwith n-type doped layer 108 and p-type doped layer 110, respectively.The electrodes are configured to provide electrical energy to epitaxialstructure 104. When a voltage is applied between first electrode 114 andsecond electrode 116, an electric current flows from the secondelectrode to the first electrode through epitaxial substrate 102 and ishorizontally distributed in epitaxial structure 104. Thus, a number ofphotons are generated by a photoelectric effect in epitaxial structure104. Horizontal light emitting diode 100 emits light from epitaxialstructure 104 due to the horizontally distributed electric current.

A manufacturing process of horizontal light emitting diode 100 issimple. However, horizontal light emitting diodes can cause severalproblems such as, but not limited to, current crowding problems,non-uniformity light emitting problems, and thermal accumulationproblems. These problems may decrease the light emitting efficiency ofthe horizontal light emitting diode and/or damage the horizontal lightemitting diode.

To overcome some of the above mentioned problems, vertical lightemitting diodes have been developed. FIG. 2 illustrates a schematic viewof a conventional vertical light emitting diode. Vertical light emittingdiode 200 includes epitaxial structure 204 and electrode unit 206disposed on the epitaxial structure for providing electrical energy.Similar to horizontal light emitting diode 100 shown in FIG. 1,epitaxial structure 204 can be made of GaN-based semiconductor materialor InGaN-based semiconductor material by an epitaxial growth process.During the epitaxial growth process, the GaN-based semiconductormaterial and the InGaN-based semiconductor material epitaxially grows upfrom an epitaxial substrate (not shown) to form n-type doped layer 208,light emitting structure 212, and p-type doped layer 210. Then,electrode unit 206 is bonded to epitaxial structure 204 after strippingthe epitaxial substrate. Electrode unit 206 includes first electrode 214and second electrode 216. First electrode 214 and second electrode 216are in ohmic contact with n-type doped layer 208 and p-type doped layer210, respectively. In addition, second electrode 216 can adhere to heatdissipating substrate 202 so as to increase the heat dissipationefficiency. When a voltage is applied between first electrode 214 andsecond electrode 216, an electric current vertically flows. Thus,conventional vertical light emitting diode 200 can effectively improvethe current crowding problem, the non-uniformity light emitting problemand the thermal accumulation problem of horizontal light emitting diode100. However, a shading effect of the electrodes is a problem in theconventional vertical light emitting diode depicted in FIG. 2. Inaddition, the manufacturing process for forming vertical light emittingdiode 200 may be complicated. For example, epitaxial structure 204 maybe damaged by high heat when adhering second electrode 216 to heatdissipating substrate 202.

In recent years, wide-bandgap nitride-based LEDs with wavelength rangefrom the ultraviolet to the shorter wavelength parts of the visiblespectra have been developed. LED devices can be applied to new displaytechnologies such as traffic signals, liquid crystal display TVs, andbacklights of cell phones. Due to the lack of native substrates, GaNfilms and related nitride compounds are commonly grown on sapphirewafers. Conventional LEDs (such as those described above) areinefficient because the photons are emitted in all directions. A largefraction of light emitted is limited in the sapphire substrate andcannot contribute to usable light output. Moreover, the poor thermalconductivity of the sapphire substrate is also a problem associated withconventional nitride LEDs. Therefore, freestanding GaN optoelectronicswithout the use of sapphire is a desirable technology that solves thisproblem. The epilayer transferring technique is a well-known innovationin achieving ultrabright LEDs. Thin-film p-side-up GaN LEDs with highlyreflective reflector on silicon substrate made by a laser lift-off (LLO)technique, combined with n-GaN surface roughening, have been establishedas an effective tool for nitride-based heteroepitaxial structures toeliminate the sapphire constraint. The structure is regarded as a goodcandidate for enhancing the light extraction efficiency of GaN-basedLEDs. However, this technique is also subject to the electrode-shadingproblem. The emitted light is covered and absorbed by the electrodes,which results in reduced light efficiency.

Thin-film n-side-up devices GaN LEDs with interdigitated imbeddedelectrodes may improve light emission by reducing some of theelectrode-shading problem. While thin-film n-side-up devices GaN LEDsprovide enhanced properties compared to thin-film p-side-up devices GaNLEDs, there is still a need for improved structures and processes formaking both p-side-up and n-side-up devices.

SUMMARY

In certain embodiments, a method for forming a plurality ofsemiconductor light emitting devices includes forming an epitaxial layeron a first temporary substrate. The epitaxial layer includes a firsttype doped layer, a light emitting layer, and a second type doped layer.The epitaxial layer is separated into a plurality of epitaxialstructures on the first temporary substrate. A second temporarysubstrate is coupled to an upper surface of the epitaxial layer with afirst adhesive layer. The first temporary substrate is removed from theepitaxial layer to expose a bottom surface of the epitaxial layer. Apermanent semiconductor substrate is coupled to the bottom surface ofthe epitaxial layer with a second adhesive layer. The second temporarysubstrate and the first adhesive layer are removed from the uppersurface of the epitaxial layer. The permanent semiconductor substrate isseparated into a plurality of portions with each portion correspondingto at least one of the plurality of epitaxial structures to form aplurality of semiconductor light emitting devices.

In some embodiments, the epitaxial layer is diced to separate theepitaxial layer into the plurality of epitaxial structures. In someembodiments, the permanent semiconductor substrate is diced to separatethe permanent semiconductor substrate into the plurality of portions. Insome embodiments, a laser is used to separate the epitaxial layer intothe plurality of epitaxial structures. In some embodiments, a laser isused to separate the permanent semiconductor substrate into theplurality of portions. In some embodiments, the epitaxial structures areused as a guide for dicing the permanent semiconductor substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the methods and apparatus of the presentinvention will be more fully appreciated by reference to the followingdetailed description of presently preferred but nonetheless illustrativeembodiments in accordance with the present invention when taken inconjunction with the accompanying drawings in which:

FIG. 1 illustrates a schematic view of a conventional horizontal lightemitting diode.

FIG. 2 illustrates a schematic view of a conventional vertical lightemitting diode.

FIG. 3 depicts an embodiment of a p-side up thin film GaN (galliumnitride) LED.

FIGS. 4A-F depict an embodiment of a method for making a p-side up LED.

FIG. 5 depicts an embodiment of an n-side up thin film GaN (galliumnitride) LED.

FIGS. 6A-E depict an embodiment of a method for making an n-side up LED.

FIG. 7 depicts an embodiment of multiple epitaxial structures separatedon a first substrate.

FIG. 8 depicts the embodiment of FIG. 7 bonded to a second substratewith a first adhesive layer.

FIG. 9 depicts the embodiment of FIG. 8 with the first substrate removedfrom the epitaxial structures.

FIG. 10 depicts the embodiment of FIG. 9 with a third substrate bondedto the epitaxial structures with a second adhesive layer.

FIG. 11 depicts the embodiment of FIG. 10 with the first adhesive layerand the second substrate removed from the epitaxial structures.

FIG. 12 depicts an embodiment of LEDs formed by separating the thirdsubstrate depicted in FIG. 11.

FIG. 13 depicts an embodiment of non-separated multiple epitaxialstructures on a first substrate.

FIG. 14 depicts the embodiment of FIG. 13 bonded to a second substratewith a first adhesive layer.

FIG. 15 depicts the embodiment of FIG. 14 with the first substrateremoved from the epitaxial structures.

FIG. 16 depicts the embodiment of FIG. 15 with a third substrate bondedto the epitaxial structures with a second adhesive layer.

FIG. 17 depicts the embodiment of FIG. 16 with the first adhesive layerand the second substrate removed from the epitaxial structures.

FIG. 18 depicts an embodiment of LEDs formed by separating the epitaxialstructures and the third substrate depicted in FIG. 17.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Thedrawings may not be to scale. It should be understood that the drawingsand detailed description thereto are not intended to limit the inventionto the particular form disclosed, but to the contrary, the intention isto cover all modifications, equivalents and alternatives falling withinthe spirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF EMBODIMENTS

In the context of this patent, the term “coupled” means either a directconnection or an indirect connection (e.g., one or more interveningconnections) between one or more objects or components.

FIG. 3 depicts an embodiment of a p-side up thin film GaN (galliumnitride) LED. P-side up LED 300 includes p-doped layer GaN layer 302,light emitting layer 304, and n-doped GaN layer 306. Light emittinglayer 304 may be, for example, a multiple quantum well layer. In someembodiments, undoped GaN layer 307 is coupled to the bottom surface ofn-doped layer 306. Layer 307 may be an epitaxial buffer layer. In someembodiments, layer 302 has a roughened upper surface and/or layer 307has a roughened lower surface (e.g., a surface roughened by wetetching). Roughening of the surfaces may increase light emissionefficiency of the layers.

The lower surface of layer 307 is bonded to reflective layer 310 withadhesive layer 308. Reflective layer 310 may be attached to substrate312. Adhesive layer 308 may be a glue material with a low refractiveindex (e.g., refractive index of about 1.4). Reflective layer 310 mayinclude a distributed Bragg reflector (DBR), an omni-directionalreflector (ODR), silver, aluminum, titanium, and/or other reflectivemetals. Substrate 312 may include silicon, silicon oxide, metal,ceramic, polymer, or other suitable substrate materials with highthermal conductivity. Substrate 312 made of silicon may have a thermalconductivity of, for example, about 168 W/mK.

First electrode 314 and second electrode 316 may be formed on p-dopedlayer 302 and n-doped layer 306, respectively. Thus, first electrode 314is a contact for layer 302 and second electrode 316 is a contact forlayer 306. Because electrodes 314, 316 are formed on top of layers 302,306, the electrodes may shade portions of the underlying layers andreduce the light emitting efficiency of LED 300. In some embodiments,layer 318 is formed on top of p-doped layer 302. Layer 318 may be atransparent conducting layer for current spreading. For example, layer318 may include indium tin oxide (ITO). The upper surface of layer 318may be roughened.

FIGS. 4A-F depict an embodiment of a method for making a p-side up LEDsuch as LED 300. FIG. 4A depicts epitaxial structure 402 formed on firstsubstrate 400. First substrate 400 may be a temporary substrate such asa sapphire substrate. Epitaxial structure 402 may be formed on firstsubstrate 400 using conventional epitaxial techniques known in the artsuch as metal organic chemical vapor deposition (MOCVD). Epitaxialstructure 402 may include undoped layer 404, first doped layer 406,light emitting layer 408, and second doped layer 410. In certainembodiments, undoped layer 404, first doped layer 406, light emittinglayer 408, and second doped layer 410 are gallium nitride (GaN) layersformed in multiple deposition processing steps.

Light emitting layer 408 may be, for example, a multiple quantum welllayer. In certain embodiments, first doped layer 406 is an n-type dopedlayer and second doped layer 410 is a p-type doped layer. In someembodiments, the upper surface of second doped layer 410 is roughenedby, for example, wet etching. A portion of the upper surface of firstdoped layer 406 may be exposed by patterning of light emitting layer 408and second doped layer 410. First electrode 412 may be formed on anupper surface of first doped layer 406. Second electrode 414 may beformed on an upper surface of second doped layer 410. The size and shapeof electrodes 412 and 414 may be defined using a photolithographyprocess.

After formation of epitaxial structure 402 on first substrate 400, theupper surface of the structure may be bonded to second substrate 416with first adhesive layer 418, as shown in FIG. 4B. Before or after thebonding process, the device may be flipped upside down, as shown in FIG.4B, such that undoped layer 404 is at the top of epitaxial structure 402and second doped layer 410 is at the bottom of the structure. Secondsubstrate 416 may be a temporary substrate (for example, a glasssubstrate, sapphire, or other insulating material type substrate). Firstadhesive layer 418 may be, for example, an epoxy glue, wax, SOG(spin-on-glass), photoresist, monomer, polymer, or any glue typematerial known in the art for bonding GaN layers to ceramic or glasslayers. In certain embodiments, epitaxial structure 402 is bonded tosecond substrate 416 using first adhesive layer 418 at temperaturesbetween about 200° C. and about 300° C. and pressures between about 5 kgforce and about 30 kg force for a 2 inch substrate.

Following bonding to second substrate 416, first substrate 400 isremoved from epitaxial structure 402, as shown in FIG. 4C. Firstsubstrate 400 may be removed using, for example, a laser lift-off (LLO)process. Removal of first substrate 400 exposes the, now, upper surfaceof undoped layer 404. In certain embodiments, upper surface of undopedlayer 404 is roughened, as shown in FIG. 4D. The upper surface ofundoped layer 404 may be roughened using, for example, a wet etchingprocess.

The structure depicted in FIG. 4D may then be bonded to third substrate420 with second adhesive layer 424, as shown in FIG. 4E. Before or afterthe bonding process, the device may be flipped upside down, as shown inFIG. 4E, such that third substrate 420 is at the bottom of thestructure. In certain embodiments, third substrate 420 includesreflective layer 422 on an upper surface of the substrate. Thirdsubstrate 420 may be, for example, a silicon oxide substrate or othersuitable thermally conductive substrate. Third substrate 420 may be thepermanent substrate for epitaxial structure 402. Reflective layer 422may include aluminum, titanium, and/or other reflective conductingmaterials. Second adhesive layer 424 may be the same or different fromfirst adhesive layer 418. For example, in some embodiments, firstadhesive layer 418 is an ether-based compound and second adhesive layer424 is a silicone-based or imide-based compound. In certain embodiments,bonding with second adhesive layer 418 occurs at temperatures betweenabout 150° C. and about 200° C. and pressures between about 300 kg forceand about 400 kg force for a 2 inch substrate.

Following bonding to third substrate 420, first adhesive layer 418 isremoved from epitaxial structure 402 to remove the first adhesive layerand second substrate 416 from the epitaxial structure, as shown in FIG.4F. First adhesive layer 418 and second substrate 416 may be removedusing, for example, a LLO process, an acid etching process, or anothersuitable etching process. The resulting structure, shown in FIG. 4F, isp-side up LED 426. P-side up LED 426 is an LED with second doped (p-typedoped) layer 410 at the top of epitaxial structure 402 and electrodes412, 414 exposed for use as contact pads.

FIG. 5 depicts an embodiment of an n-side up thin film GaN (galliumnitride) LED. N-side up LED 500 includes n-doped layer GaN layer 502,light emitting layer 504, and p-doped GaN layer 506. Light emittinglayer 504 may be, for example, a multiple quantum well layer. In someembodiments, undoped GaN layer 507 is coupled to the bottom surface ofp-doped layer 506. Layer 507 may be an epitaxial buffer layer. In someembodiments, layer 502 has a roughened upper surface and/or layer 507has a roughened lower surface (e.g., a surface roughened by wetetching). Roughening of the surfaces may increase light emissionefficiency of the layers.

The lower surface of layer 507 is bonded to reflective layer 510 withadhesive layer 508. Reflective layer 510 may be attached to substrate512. Adhesive layer 508 may be a glue material with a low refractiveindex (e.g., refractive index of about 1.4). Reflective layer 510 mayinclude aluminum, titanium, and/or other reflective metals. Substrate512 may include silicon, silicon oxide, or other suitable substratematerials with high thermal conductivity. Substrate 512 made of siliconmay have a thermal conductivity of, for example, about 168 W/mK.

First electrode 514 and second electrode 516 may be formed on p-dopedlayer 506 and n-doped layer 502, respectively. Thus, first electrode 514is a contact for layer 506 and second electrode 516 is a contact forlayer 502. Electrodes 514, 516 may be imbedded in LED 500 such thatthere is no electrode shading, thus increasing the emission efficiencyof the LED.

FIGS. 6A-E depict an embodiment of a method for making an n-side up LEDsuch as LED 500. FIG. 6A depicts epitaxial structure 602 formed on firstsubstrate 600 (e.g., a temporary substrate). First substrate 600 may be,for example, a sapphire substrate. Epitaxial structure 602 may be formedon first substrate 600 using conventional epitaxial techniques known inthe art such as metal organic chemical vapor deposition (MOCVD).Epitaxial structure 602 may include undoped layer 604, first doped layer606, light emitting layer 608, and second doped layer 610. In certainembodiments, undoped layer 604, first doped layer 606, light emittinglayer 608, and second doped layer 610 are gallium nitride (GaN) layersformed in multiple deposition processing steps.

Light emitting layer 608 may be, for example, a multiple quantum welllayer. In certain embodiments, first doped layer 606 is an n-type dopedlayer and second doped layer 610 is a p-type doped layer. In someembodiments, the upper surface of second doped layer 610 is roughenedby, for example, wet etching. A portion of the upper surface of firstdoped layer 606 may be exposed by patterning of light emitting layer 608and second doped layer 610. First electrode 612 may be formed on anupper surface of first doped layer 606. Second electrode 614 may beformed on an upper surface of second doped layer 610. The size and shapeof electrodes 612 and 614 may be defined using a photolithographyprocess.

After formation of epitaxial structure 602 on first substrate 600, theupper surface of the structure may be bonded to second substrate 616with first adhesive layer 618, as shown in FIG. 6B. Before or after thebonding process, the device may be flipped upside down, as shown in FIG.6B, such that undoped layer 604 is at the top of epitaxial structure 602and second doped layer 610 is at the bottom of the structure. Secondsubstrate 616 may be, for example, a silicon substrate or other suitablethermally conductive substrate. Second substrate 616 may be thepermanent substrate for epitaxial structure 602. In certain embodiments,second substrate 616 includes reflective layer 620 and/or insulatinglayer 622 on an upper surface of the substrate. Reflective layer 620 mayinclude aluminum, titanium, and/or other reflective conductingmaterials. Insulating layer 622 may include oxides, nitrides, and/orother suitable electrically insulating materials with high lighttransparency. First adhesive layer 618 may be, for example, an epoxyglue or any glue type material known in the art for bonding GaN layersto silicon or silicon oxide layers.

Following bonding to second substrate 616, first substrate 600 isremoved from epitaxial structure 602, as shown in FIG. 6C. Firstsubstrate 600 may be removed using, for example, a laser lift-off (LLO)process. Removal of first substrate 600 exposes the, now, upper surfaceof undoped layer 604.

Following removal of first substrate 600, portions of undoped layer 604and first doped layer 606 are removed to expose at least part of firstelectrode 612 and at least part of second electrode 614, as shown inFIG. 6D. Portions of undoped layer 604 and first doped layer 606 may beremoved using, for example, an anisotropic etching process such asinductively coupled plasma (ICP) reactive ion etching (RIE).

In certain embodiments, upper surface of undoped layer 604 is roughened,as shown in FIG. 6E. The upper surface of undoped layer 604 may beroughened using, for example, a wet etching process (e.g., a sodiumhydroxide wet-etching process or a phosphoric acid wet etching process).The resulting structure, shown in FIG. 6E, is n-side up LED 624. N-sideup LED 624 is an LED with first doped (n-type doped) layer 610 at thetop of epitaxial structure 602 and electrodes 612, 614 exposed for useas contact pads with the electrodes not shading light emitting layer608.

In certain embodiments, multiple LEDs (e.g., multiple epitaxialstructures) are formed on a single substrate. The multiple epitaxialstructures may be formed simultaneously on the single substrate byforming the multiple epitaxial structures from a single group of layersepitaxially deposited on the substrate. For example, epitaxial layers(e.g., the doped/undoped layers and the light emitting layer) are formed(e.g., using MOCVD) across the entire substrate and then the layers aredivided into sections to form the multiple epitaxial structures. Formingmultiple LEDs simultaneously may reduce the effects of process variationduring formation of the LEDs and produce LEDs with more uniformproperties.

There are, however, potential problems with forming multiple LEDs on asingle substrate, especially with multiple LEDs formed using theepilayer transferring technique (e.g., transferring the epitaxialstructures from a sapphire substrate to a silicon substrate as describedabove). One of the potential problems includes cracking of the epitaxialstructures due to the high pressures (e.g., above about 9.8 MPa) appliedto the structures during the bonding process. Other potential problemsinclude mixing of adhesives if two or more bonding processes are usedand gaps exist between the epitaxial structures, generation of voids inan adhesive layer, difficulty in reducing the thickness of an adhesivelayer, and/or floating of epitaxial structures during the bondingprocess.

FIGS. 7-12 depict an embodiment of a process for forming multiple p-sideup GaN LEDs on a single substrate using an epilayer transfer techniquewith the LEDs isolated before transferring of the substrates. FIG. 7depicts an embodiment of multiple epitaxial structures 402A, 402B, 402Con first substrate 400. First substrate 400 may be, for example, asapphire substrate on which epitaxial structures 402A, 402B, 402C areformed. Epitaxial structures 402A, 402B, and 402C may be formed on firstsubstrate 400 using conventional epitaxial techniques known in the artsuch as metal organic chemical vapor deposition (MOCVD). Epitaxialstructures 402A, 402B, 402C may include, respectively, first dopedlayers 406A, 406B, 406C, light emitting layers 408A, 408B, 408C, andsecond doped layers 410A, 410B, 410C. In certain embodiments, undopedlayers are located between second doped layers 410A, 410B, 410C andfirst substrate 400.

Light emitting layers 408A, 408B, 408C may be, for example, multiplequantum well layers. In certain embodiments, first doped layers 406A,406B, 406C are n-type doped layers and second doped layers 410A, 410B,410C are p-type doped layers. In some embodiments, the upper surface ofsecond doped layers 410A, 410B, 410C are roughened by, for example, wetetching. A portion of the upper surfaces of first doped layers 406A,406B, 406C may be exposed by patterning of light emitting layers 408A,408B, 408C and second doped layers 410A, 410B, 410C such that electrodesmay be placed on the upper surfaces of the first doped layers. Thus,epitaxial structures 402A, 402B, 402C may be p-side up GaN LEDstructures.

Separated (isolated) epitaxial structures may be formed by depositingthe epitaxial layers used in the epitaxial structures across thesubstrate and subsequently separating (or isolating) sections of thedeposited layers to form the separated (isolated) epitaxial structuressuch as epitaxial structures 402A, 402B, 402C depicted in FIG. 7. Adicing or cutting saw or a laser may be used to separate the epitaxiallayers and form separated epitaxial structures 402A, 402B, 402C on firstsubstrate 400. In some embodiments, an etching process is used toseparate the epitaxial layers and form separated epitaxial structures402A, 402B, 402C on first substrate 400.

Following formation of separated epitaxial structures 402A, 402B, 402Con first substrate 400, the upper surface of the epitaxial structuresmay be bonded to second substrate 416 with first adhesive layer 418, asshown in FIG. 8. For simplicity in the drawings epitaxial structures402A, 402B, 402C are referenced without the details of the individuallayers in the epitaxial structures in FIGS. 8-12. In certainembodiments, second substrate 416 is a glass substrate and firstadhesive layer 418 is an epoxy glue. As shown in FIG. 8, first adhesivelayer 418 may flow into the gaps between epitaxial structures 402A,402B, 402C.

Following bonding to second substrate 416, first substrate 400 isremoved from epitaxial structures 402A, 402B, 402C, as shown in FIG. 9.First substrate 400 may be removed using, for example, a laser lift-off(LLO) process. In some embodiments, the exposed surface of epitaxialstructures 402A, 402B, 402C is roughened by, for example, a wet etchingprocess.

After removal of first substrate 400, third substrate 420 may be bondedto epitaxial structures 402A, 402B, 402C with second adhesive layer 424,as shown in FIG. 10. In certain embodiments, third substrate 420includes a reflective layer between the substrate and second adhesivelayer 424. Third substrate 420 may be, for example, a silicon oxidesubstrate or other suitable thermally conductive substrate. Thirdsubstrate 420 may be the permanent substrate for epitaxial structures402A, 402B, 402C.

In some embodiments, as shown in FIG. 10, first adhesive layer 418 maymix with, or flow into, second adhesive layer 424 at or near the gapsbetween epitaxial structures 402A, 402B, 402C. This flow of firstadhesive layer 418 into second adhesive layer 424 may be caused by thepressure applied at elevated temperatures during bonding using thesecond adhesive layer. For example, bonding using second adhesive layer424 may take place at temperatures of at least about 200° C. and withapplied pressures above about 9.8 MPa. At such temperatures andpressures, first adhesive layer 418 may mix with second adhesive layer424 in the gaps between epitaxial structures 402A, 402B, 402C becausethe adhesive layers contact each other in these gaps.

Because of the mixing of first adhesive layer 418 with second adhesivelayer 424, voids 450 may be formed in the second adhesive layer when thefirst adhesive layer and second substrate 416 are removed from epitaxialstructures 402A, 402B, 402C, as shown in FIG. 11. First adhesive layer418 and second substrate 416 may be removed from epitaxial structures402A, 402B, 402C using, for example, an acid etching process. Voids 450are formed at or near the gaps between epitaxial structures 402A, 402B,402C. These voids may contribute to cracking of epitaxial layers inepitaxial structures 402A, 402B, 402C during subsequent processing. Forexample, the epitaxial layers may crack during wire bonding of contactpads as the wire bonding pads may be located above voids 450.

In certain embodiments, mixing of first adhesive layer 418 with secondadhesive layer 424 is inhibited if the melting point of the firstadhesive layer is higher than the melting point of the second adhesivelayer. If the melting point of first adhesive layer 418 is higher thanthe melting point of second adhesive layer 424, the first adhesive layermay remain solidified during the bonding process using the secondadhesive layer and inhibit mixing between the adhesive layers. Thus, ifthe melting point of first adhesive layer 418 is higher than the meltingpoint of second adhesive layer 424, formation of voids 450, depicted inFIG. 11, may be inhibited.

After removal of first adhesive layer 418 and second substrate 416 fromepitaxial structures 402A, 402B, 402C, light emitting devices (LEDs)426A, 426B, 426C may be formed by separating third substrate 420 incorrespondence with epitaxial structures 402A, 402B, 402C, as shown inFIG. 12. Third substrate 420 may be separated using, for example, adicing (cutting) saw or a laser. In some embodiments, an etching processis used to separate third substrate 420. Third substrate 420 isseparated along lines that correspond to the gaps between epitaxialstructures 402A, 402B, 402C. In some embodiments, epitaxial structures402A, 402B, 402C are used as a guide for separating third substrate 420.Thus, LED 426A includes epitaxial structure 402A and substrate 420A, LED426B includes epitaxial structure 402B and substrate 420B, and LED 426Cincludes epitaxial structure 402C and substrate 420C.

FIGS. 13-18 depict an embodiment of a process for forming multiplep-side up GaN LEDs on a single substrate using an epilayer transfertechnique with the LEDs isolated after transferring of the substrates.FIG. 13 depicts an embodiment of multiple epitaxial structures 402A,402B, 402C on first substrate 400. First substrate 400 may be, forexample, a sapphire substrate on which epitaxial structures 402A, 402B,402C are formed. Epitaxial structures 402A, 402B, and 402C may be formedon first substrate 400 using conventional epitaxial techniques known inthe art such as metal organic chemical vapor deposition (MOCVD).Epitaxial structures 402A, 402B, 402C may include, respectively, firstdoped layers 406A, 406B, 406C, light emitting layers 408A, 408B, 408C,and second doped layers 410A, 410B, 410C. In certain embodiments,undoped layers are located between second doped layers 410A, 410B, 410Cand first substrate 400.

Light emitting layers 408A, 408B, 408C may be, for example, multiplequantum well layers. In certain embodiments, first doped layers 406A,406B, 406C are n-type doped layers and second doped layers 410A, 410B,410C are p-type doped layers. In some embodiments, the upper surface ofsecond doped layers 410A, 410B, 410C are roughened by, for example, wetetching. A portion of the upper surfaces of first doped layers 406A,406B, 406C may be exposed by patterning of light emitting layers 408A,408B, 408C and second doped layers 410A, 410B, 410C such that electrodesmay be placed on the upper surfaces of the first doped layers.

As shown in FIG. 13, however, epitaxial structures 402A, 402B, 402C havenot yet been separated or isolated. The dashed lines in FIG. 13 (and inFIGS. 14-17) represent the lines along which epitaxial structures 402A,402B, 402C will later be separated. Thus, in FIGS. 13-17, first dopedlayers 406A, 406B, 406C are a continuous first doped layer while seconddoped layers 410A, 410B, 410C and light emitting layers 408A, 408B, 408Care separated due to the patterning to expose the upper surfaces of thefirst doped layers for electrodes.

Following formation of epitaxial structures 402A, 402B, 402C on firstsubstrate 400, the upper surface of the epitaxial structures may bebonded to second substrate 416 with first adhesive layer 418, as shownin FIG. 14. For simplicity in the drawings epitaxial structures 402A,402B, 402C are referenced without the details of the individual layersin the epitaxial structures in FIGS. 14-18. In certain embodiments,second substrate 416 is a glass substrate and first adhesive layer 418is epoxy glue. As epitaxial structures 402A, 402B, 402C have not beenseparated, there are no gaps for first adhesive layer 418 to flowbetween the epitaxial structures.

Following bonding to second substrate 416, first substrate 400 isremoved from epitaxial structures 402A, 402B, 402C, as shown in FIG. 15.First substrate 400 may be removed using, for example, a LLO process. Insome embodiments, the exposed surface of epitaxial structures 402A,402B, 402C is roughened by, for example, a wet etching process.

After removal of the first substrate, third substrate 420 may be bondedto epitaxial structures 402A, 402B, 402C with second adhesive layer 424,as shown in FIG. 16. In certain embodiments, third substrate 420includes a reflective layer between the substrate and second adhesivelayer 424. Third substrate 420 may be, for example, a silicon oxidesubstrate or other suitable thermally conductive substrate. Thirdsubstrate 420 may be the permanent substrate for epitaxial structures402A, 402B, 402C.

There is relatively little or no potential for mixing between firstadhesive layer 418 and second adhesive layer 424 during the bondingprocess shown in FIG. 16 because there are no gaps between epitaxialstructures 402A, 402B, 402C. Additionally, there is no possibility forepitaxial structures 402A, 402B, 402C floating during either of thebonding processes because the epitaxial structures have not beenseparated. During the bonding process shown in FIG. 16, the pressureapplied to epitaxial structures 402A, 402B, 402C may be increased tohigher pressures than the embodiment described above in FIG. 10. Thepressure can be increased to higher pressures because epitaxialstructures 402A, 402B, 402C have not been separated and there is littleor no potential for mixing of the glues between the epitaxialstructures. Bonding at higher pressure may reduce the thickness ofsecond adhesive layer 424 during and after the bonding process. Reducingthe thickness of second adhesive layer 424 may increase the lightemitting efficiencies of LEDs made from epitaxial structures 402A, 402B,402C.

After bonding of third substrate 420 to epitaxial structures 402A, 402B,402C, first adhesive layer 418 and second substrate 416 are removed fromthe epitaxial structures, as shown in FIG. 17. First adhesive layer 418and second substrate 416 may be removed using, for example, an LLOprocess or an acid etching process.

After removal of first adhesive layer 418 and second substrate 416 fromepitaxial structures 402A, 402B, 402C, the epitaxial structures andthird substrate 420 are separated along the dashed lines (shown in FIG.17) to form LEDs 426A, 426B, 426C, as shown in FIG. 18. Epitaxialstructures 402A, 402B, 402C and third substrate 420 may be separatedusing, for example, a dicing (cutting) saw or a laser. In someembodiments, an etching process is used to separate epitaxial structures402A, 402B, 402C and third substrate 420. As shown in FIG. 18, LED 426Aincludes epitaxial structure 402A and substrate 420A, LED 426B includesepitaxial structure 402B and substrate 420B, and LED 426C includesepitaxial structure 402C and substrate 420C.

As shown in the embodiment depicted in FIGS. 7-12 and the embodimentdepicted in FIGS. 13-18, multiple LEDs may be formed on a singlesubstrate using an epilayer transfer technique. In certain embodiments,the epitaxial layers in epitaxial structures 402A, 402B, 402C depictedin FIGS. 7-12 may be thinner than the epitaxial layers in epitaxialstructures 402A, 402B, 402C depicted in FIGS. 13-18. The epitaxiallayers in epitaxial structures 402A, 402B, 402C depicted in FIGS. 13-18may have to be thicker to inhibit cracking of the epitaxial layersduring the bonding process. For example, the portions of first dopedlayers 406A, 406B, 406C with exposed upper surfaces may have potentialfor cracking during the bonding process if the layers are too thin.Because of the gaps between epitaxial structures 402A, 402B, 402Cdepicted in FIGS. 7-12, the adhesive layers have area to flow into andrelieve the pressure applied to the thinner areas of the epitaxiallayers. This pressure relief may allow thinner epitaxial layers to beused.

It is to be understood the invention is not limited to particularsystems described which may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used in this specification, the singular forms “a”, “an”and “the” include plural referents unless the content clearly indicatesotherwise. Thus, for example, reference to “a device” includes acombination of two or more devices and reference to “a material”includes mixtures of materials.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as the presently preferred embodiments. Elements andmaterials may be substituted for those illustrated and described herein,parts and processes may be reversed, and certain features of theinvention may be utilized independently, all as would be apparent to oneskilled in the art after having the benefit of this description of theinvention. Changes may be made in the elements described herein withoutdeparting from the spirit and scope of the invention as described in thefollowing claims.

1. A method for forming a plurality of semiconductor light emittingdevices, comprising: forming an epitaxial layer comprising a first typedoped layer, a light emitting layer, and a second type doped layer on afirst temporary substrate; separating the epitaxial layer into aplurality of epitaxial structures on the first temporary substrate;coupling a second temporary substrate to an upper surface of theepitaxial layer with a first adhesive layer; removing the firsttemporary substrate from the epitaxial layer to expose a bottom surfaceof the epitaxial layer; coupling a permanent semiconductor substrate tothe bottom surface of the epitaxial layer with a second adhesive layer;removing the second temporary substrate and the first adhesive layerfrom the upper surface of the epitaxial layer; and separating thepermanent semiconductor substrate into a plurality of portions with eachportion corresponding to at least one of the plurality of epitaxialstructures to form a plurality of semiconductor light emitting devices.2. The method of claim 1, further comprising cutting the epitaxial layerto separate the epitaxial layer into the plurality of epitaxialstructures.
 3. The method of claim 1, further comprising cutting thepermanent semiconductor substrate to separate the permanentsemiconductor substrate into the plurality of portions.
 4. The method ofclaim 3, further comprising using the epitaxial structures as a guidefor cutting the permanent semiconductor substrate.
 5. The method ofclaim 1, further comprising using a laser to separate the epitaxiallayer into the plurality of epitaxial structures.
 6. The method of claim1, further comprising using a laser to separate the permanentsemiconductor substrate into the plurality of portions.
 7. The method ofclaim 1, further comprising etching the epitaxial layer to separate theepitaxial layer into the plurality of epitaxial structures.
 8. Themethod of claim 1, further comprising etching the permanentsemiconductor substrate to separate the permanent semiconductorsubstrate into the plurality of portions.
 9. The method of claim 1,further comprising forming a reflective layer between the permanentsemiconductor substrate and the second adhesive layer.
 10. The method ofclaim 1, further comprising forming a plurality of contact pads on thefirst doped layer and a plurality of contact pads on the second dopedlayer such that each semiconductor light emitting device has at leastone contact pad on the first doped layer and at least one contact pad onthe second doped layer.
 11. The method of claim 1, wherein the firsttype doped layer comprises p-type doped GaN and the second type dopedlayer comprises p-type doped GaN.
 12. The method of claim 1, wherein thelight emitting layer comprises a multiple quantum well structure. 13.The method of claim 1, wherein the permanent semiconductor substratecomprises silicon.
 14. The method of claim 1, wherein the firsttemporary substrate comprises sapphire.
 15. The method of claim 1,wherein the second temporary substrate comprises glass.
 16. The methodof claim 1, wherein the epitaxial layer further comprises an undopedlayer below the first type doped layer.
 17. The method of claim 1,further comprising roughening the bottom surface of the epitaxial layer.18. The method of claim 1, further comprising bonding the secondtemporary substrate to the upper surface of the epitaxial layer with thefirst adhesive layer.
 19. The method of claim 1, further comprisingbonding the permanent semiconductor substrate to the bottom surface ofthe epitaxial layer with the second adhesive layer.
 20. The method ofclaim 1, further comprising removing the first temporary substrate fromthe epitaxial layer to expose a bottom surface of the epitaxial layerusing a laser lift off process.
 21. The method of claim 1, furthercomprising removing the second temporary substrate and the firstadhesive layer from the upper surface of the epitaxial layer using anacid etching process.
 22. The method of claim 1, wherein the firstadhesive layer has a higher melting point than the second adhesivelayer.